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• FFmpeg Decklink playout audio PCM

  28 décembre 2019, par Rick Jansen

  I’m working on a ffmpeg playout application for Decklink but I’m facing some audio issues. I’ve seen other questions about this topic but none of them are currently helping.

  I’ve tried Reubens code (https://stackoverflow.com/a/15372417/12610231) with the swr_convert for playing out ffmpeg/libav frames to a Decklink board (this needs to be 16 bits PCM interleaved) but the audio sounds wrong. It sounds like it’s missing samples/ only getting half of the required samples).

  When I record the samples in a raw audio file and play it out with Audacity the timeline is half the length of the actual recording and playing the samples on double speed.

  I also tried the ’manual’ conversion (https://stackoverflow.com/a/15372417/12610231) but unfortunately, not the result I was hoping for.

  Here are some snippets of my code

  swr_ctx = swr_alloc();
  
  av_opt_set_int(swr_ctx, "in_channel_count", pAudioCodecCtx->channels, 0);
  
  av_opt_set_int(swr_ctx, "in_sample_rate", pAudioCodecCtx->sample_rate, 0);
  
  av_opt_set_int(swr_ctx, "in_channel_layout", pAudioCodecCtx->channel_layout, 0);
  
  av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", pAudioCodecCtx->sample_fmt, 0);
  
  av_opt_set_int(swr_ctx, "out_channel_count", 2, 0);
  
  av_opt_set_int(swr_ctx, "out_sample_rate", 48000, 0);
  
  av_opt_set_int(swr_ctx, "out_channel_layout", AV_CH_LAYOUT_STEREO, 0);
  
  av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", AV_SAMPLE_FMT_S16, 0);
  
  
  
  if (swr_init(swr_ctx))
  
  {
  
      printf("Error SWR");
  
  }

  ///

  ret = avcodec_decode_audio4(pAudioCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
  if (ret < 0) {
  
      printf("Error in decoding audio frame.\n");
  
  }
  
  
  
  swr_convert(swr_ctx, (uint8_t**)&m_audioBuffer, pFrame->nb_samples, (const uint8_t *)pFrame->extended_data, pFrame->nb_samples);

  It also looks like that the FFmpeg packet contains out of 1 video packet en 2 audio packets, not sure what to do with the second audio packet, I already tried to combine the first and second audio package without any good result on the audio side.

  Any help is appreciated.

• Speed Up Creation of M3U8 - FFMPEG

  6 septembre 2017, par Kenny Johnson

  we are using ffmpeg to take rtsp video and create an m3u8 so we can stream the video to phones and computers via HLS using Clappr player.

  It works but it takes about 15 seconds for the m3u8 to be created.

  We have tried everything we can think of to speed it up. Just trying to get the video to start quicker.

  Right now it takes about 15 seconds for the video to start. We need to cut it in half.

  Our keyframe and chunk size are both set to 3 right now.

  Anyone have any suggestions ?
  Thanks for your time !

• merge/combine two FFMPEG commands together into one command

  26 février 2021, par Mayank Thapliyal

  I have been processing videos for a while and I have been using ffmpeg to make my life easy. But there are two commands which I want to combine into single command :-

  


  Step 1 :- Divide a video vertically into two parts and then stack them horizontally

  


  ffmpeg -i usa.mp4 -filter_complex "[0]crop=iw:ih/2:0:0[top];[0]crop=iw:ih/2:0:oh[bottom];[top][bottom]hstack" -preset fast -c:a copy usa$.mp4

  


  Step 2 :- Combine 3 videos into single video (the video from Step 1 will be in between the start.mp4 and end.mp4)

  


  ffmpeg -i start.mp4 -i usa$.mp4 -i end.mp4 -vsync 2 -filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" usa_.mp4

  


  Can anyone please combine the videos into single command.I will be then able to save a lot of computing time(I guess that)

  


  Thanks in advance